Siren Song
by The Fictionist
Summary: Siren/Merfolk AU. Harry is a sailor. Tom is a siren.
1. Chapter One

The creatures had terrorized the coastal towns, his own included, for as long as he could remember.

They'd taken his parents, and so many other people's families too in an endless war of land and sea, staining the morning tide crimson.

It always started the same - the beautiful, haunting siren song that drifted in like a thick fog, winded its way through the streets, crept into your head and stole your soul away in the night. People tried to block their ears, with anything available, but it whispered in either way, as soft as a lover's kiss.

Anyone who was stupid enough to be out after dark was instantly caught, and getting stuck out at sea was unthinkable, and sometimes they came at day too.

It drifted along now, like a collar and leash, as he clamped his hands over his ears, desperate not to hear and die. His throat felt thick, his muscles rigid as it pervaded his senses either way.

He knew the Dursleys didn't like him, resented having him, but he never thought they'd go as far as set it up that he would be stuck outside like this.. He felt sick, his body electric with terror.

He'd been sent to work in the caves at the end of the beach, just like he did so very often for his Uncle's mining company, only this time, he'd stayed too late in the darkness, knowing he needed to get his work done if he wanted to avoid trouble.

Now he was in even bigger trouble, as he scrambled up the slippery rocks at the cave's entrance, struggling for purchase as the tide rolled in. It was already up to his waist, and tearing along the beach.

He wondered if he could still get out, dart across the waves, he wasn't a bad swimmer, or if he'd just get hurled against the rocky pier by the power of the ocean. Probably the latter.

He suddenly had the terrible certainty that he was going to drown, and he swallowed thickly - wondering if he could maybe even find somewhere high enough upon these slippery rocks to cling to.

Then the song started, and he clung tighter, the waves starting to crash against him with a greater speed.

He didn't...fear death, but that didn't mean he necessarily welcomed it. He was eight year's old, he had so much more to live for then-heads. There were heads in the water, starting to surround him, watching him.

His posture went rigid, even paler them before, and he was already cold in the water.

"Well, well," a voice murmured, like liquid velvet, "we don't normally get one's as young as you. You're all skin and bone."

Harry's head whipped around, his jaw clenched.  
It was the first time he'd ever seen one of them - this one had dark hair and even darker eyes, and skin pale and ethereal like slices of the moon. Harry also caught a glimpse of handsome scarlet scales in the water, then more firmly as the creature pulled itself to rest on the rocks too, right in front of him. It was male.

"I'll give you blood poisoning," Harry said, immediately, not even thinking about it. "I honestly taste horrible. All sorts of infections. And skin and bone like you said, no fat, you don't want me. Really."

It blinked, slowly, head tilting to one side, humming.

"Interesting," it said, after a moment. "You're immune to my song. What's your name?"  
Harry stared, trying not to flinch as another wave crashed down over him and the slippery rock, coughing.

"Harry."

"Pleasure to meet you, Harry," it purred. "You can call me Tom." It circled him once more, studying him with those unnerving, dark eyes. "And you seem to be in rather a predicament, don't you? How long do you think, Harry, until the tide smashes you against the rocks like a brained fish?"  
It reached out, running fingers over his trembling muscles. "You're tired already." The tone was mockingly sympathetic, and Harry hated it, snarling.

What he hated even more was how easily Tom manipulated the waters, seeming largely unbothered by the currents, overpowering them, resting against the rock once more.

"But you could help me get to shore."

"I could," the other agreed, but Harry couldn't help but be uneasily aware of more and more heads surfacing in the water around them, with hungry eyes. He swallowed. "I could also find myself a truly lovely meal..."

A hand ghosted across his cheek, and the next second it had disappeared, reappearing right next to him, cold, wet skin and scales against his back as the waves continued to crash down.

"You could just slip away," it whispered, against his ear. "You clearly don't have all that much left to you if a little thing like is left alone on these rocks. Where's your clan?"

"Dead. Your people killed them." He jutted his chin up, wishing he could shove the creature away, but daring not to let go of the rocks for toppling straight into the churning waters around him.

"Hmm, poor thing," the creature murmured, and though there was nothing in the tone to directly indicate it, Harry was certain he was being mocked again. Its fingers stroked through his wet hair, and the next second, 'Tom' was in front of him again, a smirk upon his lips. "What do I get, Harry, if I help you to the shore?"

"I-I don't-" Harry began, confused. He didn't have a clue what the creature wanted, or why it didn't just kill him when he was so obviously easy pickings.

"Tell you what," Tom interrupted, smirk broadening. "Why don't we make a deal. You're how old...seven? Eight?"

"Eight," Harry said warily, not sure if he should be curious or just more unnerved. The next wave loosened his grip, and he would have crashed against the rocks if not for the arms suddenly around him, cradling his spluttering, sodden form.

The merfolk around them swam and circled a little closer, and the quiet music still rung in his ears. It was something ungodly, unearthly, deadly and the most beautiful sound he'd ever heard all the same. Part of him wondered if he wasn't dead already.

"Well, I'm sure it's evident to you by now that you are dead without my generous assistance," Tom murmured, voice never going above that soft silkiness. "I could drag you under any second-" as if to prove it, the creature dunked his head harshly under the water, holding it just below the surface for a moment or two before he resurfaced, "-or just let you smash against the rocks."

"What do you want?" Harry bit out, eyes tight. "I don't have any gold."

"Ten years."

"Sorry, what?" Harry's brow furrowed.

"My deal is ten years. I'll help you out, and you get ten years to live on the surface. Then you're mine."

"What do you mean, then I'm yours?" Harry's eyes widened, as he twisted against the grip holding him close. The creature just swam out a little more, away from the immediate danger of the rocks.

"Then it means I will come for you. And your current existence will cease."

What, was this type of sick thing about fattening up - or in this case, letting him get a bit bigger - the food source, or something?

But he didn't have to come back. It wasn't like Tom could leave the water, he could just...disappear. And at the moment he was dead anyway, so if such a thing was inevitable, he might as well live a little longer. He didn't know. But he didn't want to die like this, here and now.

"Twenty years?" he tried, hopefully.

"Ten. Or no deal."  
Harry's brow furrowed, and he wondered if he should be concerned about the insistence on that number in particular. He swallowed, and the creature let it's grip slip a little, and the other creatures immediately surged forwards like he was a piece of dropped fish food.

"Ten!" he yelled. "I'll go with ten - just, just get me out of here."

He was spun around again, and Tom's eyes were gleaming in the darkness of the evening. He was surprised when the creature pressed a sharp kiss to his forehead, giving him a flash of pearly, razor sharp teeth, followed by a throbbing headache.

"What did you just-?"  
The other creatures around them had immediately backed off, watching them both with cold eyes.

"You can call it a little insurance, that's all. Take a deep breath now."

"Why-?"  
He was underwater, and Harry immediately panicked that Tom had gone against his word, struggling and thrashing, trying to break the surface again. The creature's grip just tightened further, almost bruising against his arms, and water was rushing through his ears and he had to squeeze his eyes shut and - and - he was coughing and the wind was whipping through his hair again with a salty spring, and there was solid land beneath him.

His head whipped around again, to see Tom retreating back into the waters, as he himself clambered more firmly up the beach from the smaller waves chasing his ankles.

"Run along now, little human," the creature purred. "I'll be seeing you."  
Then he was gone.

* * *

They called him the Boy Who Lived now. They said he could get rid of the creatures, the threat, the sirens, that drew people to the coast and drowned them, because he was the boy deaf to siren song.

He wasn't sure he believed he could end them.  
He knew, in his heart, that the creatures slaughtered and fed on the hearts of so many couldn't possibly be good, but that didn't stop the melody from washing in and out of his mind like the waves lapping the shore. That didn't stop him from remembering that Tom had helped him, when he could have simply killed him.

He didn't know.  
Tom had also made that deal.

The Dursleys had been shocked and outraged when he was found outside the door next morning, shivering and wet, but very much alive still.

They said he was a freak of nature, so rotten that even the mermaids and merfolk didn't want him.

But he hadn't been home for a very long time now though; he'd joined Hogwarts Navy training when he was eleven, and, it was there that he met Albus Dumbledore.

Upon hearing his story and name, and his reasoning for wanting to join the academy, the old man had immediately taken a keen interest in him.

It was only year's later that he found out why.

"What the hell do you mean I'm going to become one of them? That I'm chosen?" he demanded, bewildered. He was fifteen, and sitting in a chair in the Admiral's office.

"Only certain people can become one of them...those that are immune to their song. That's about one person in a hundred. These people are also the only people who can actually kill the creatures too," Dumbledore explained, quietly. "They're typically marked in some way at a young age, claimed by the one that intends to turn them and take them."

"But I met one," Harry said, somewhere between horror and something else. "He let me go-" the deal. Ten years. The words haunted him some more at every birthday, but that was ridiculous. Tom couldn't exactly come out of the water and drag him down into the deep...could he?

Dumbledore watched his expression carefully.

"There's a certain age needed, for the process, a short few years between the ages of eighteen and twenty one, in which you will have the capacity to both kill the creatures, but also become one, if the one with such intention finds you - and believe me, if you've been marked, you will be hunted."

"But surely I could just stay on land between that age and I'd be fine?"

"Yes, but they're petty creatures, and if you spite the deal, they will never stop hunting you until the end of your days."

"Well, so long as I'm not on sea-" he stopped. He loved the sea, now he wondered if that was a symptom, but the fact remained. More so, he'd been in training since he was eleven, what else was there for him? He swallowed.

"You'll be bonded by now. It's any water that you're near, that the creature can appear in. He can't come out, and a glass of water for example isn't very substantial, and it is literally only in the sea. But you'd be able to hear its voice, and so would everyone around you. If it sings..."

"People will dunk their heads into the water source, and, if it's big enough, they'll drown," Harry finished, going cold. "People will drown wherever they go."

He felt like the footing, everything he'd been relying on, had been yanked out from beneath his feet.

"What do I do? How do you know all of this?"

"I had a...friend," Dumbledore replied, eyes growing distant, sorrowful. "He was my first mate. Gellert, he was called. Gellert Grindelwald. He'd been marked too, and in a similar situation."

"What happened?"  
Harry had a bad feeling.

"He made the change," Dumbledore bit out. "He'd always rather liked the idea of immortality, of power and ownership over the seas. You've got to understand, Harry, this has been going on for years...this endless war between sea and land, with millions of casualties on our side." Harry was pretty sure he had brain freeze, and Dumbledore was studying him carefully. "Your mother, Lily, was marked too."

Harry's head snapped up at that, eyes wide.  
"Is she-?" Was she one of them now?

"She didn't want to make the change. It would mean living past all of her friends, and she would never have been able to have you, to have children, due to certain anatomical changes. There was also the matter of what the creatures feed on, and what they do, which as you can imagine, she found objectionable."

"I'm sensing a but," Harry bit out, mind prickling with all of the new knowledge, the sheer enormity of the whole thing. How had he never known before? He'd just been told that his parents were murdered!

"Your father, James, was murdered when you were just a child," Dumbledore said. "He was a Captain of his own ship, the Marauder, and the sirens, the merfolk, whichever you wish to call the creatures, attacked the boat, and picked off everyone in it. Including your father. It was supposed to be his last mission, but he never got home to your mother, who was pregnant with you at the time."

"And what happened to her?"

"She had a child to protect, and it was clear to her too that everyone around her was in danger - whether they were in her close proximity to be drowned or not. She didn't want to raise a child in that environment. So she went out to sea, and they took her, and she starved, guiding sailors away from ships."

"I could do that."

"You could also get out your deal by killing the one who gave it to you. You can't live as human whilst the creature survives."

Harry went quiet at that, before standing up.  
"Thank you for your honesty, sir."

His path was set.

* * *

Harry graduated at seventeen, and soon became Captain of his own ship Green Lightning. He travelled for several years, largely successful in his endeavours and tasks, fighting against the creatures...but conditions only continued to get worse.

There was just more rumours of ships disappearing, of coastal towns wiped out and sailors going missing. And he himself, now nineteen, could no longer afford to keep a crew when they all just sank to watery graves.

The deaths of his first mates, Ron and Hermione, hit him the hardest. He should never have let them come with him. He'd said that at the beginning, but they wouldn't listen.

And everywhere he was followed by that beautiful song which pervaded both his dreams and nightmares.

On land, there were talks of sacrifice, that maybe a select group of humans offered for both turning and eating a year would appease the relentless hunt, and save the majority. It wasn't the worst fate they said, for the creatures themselves were so breathtaking. Harry snorted at the irony of the description, and thought the so called 'solution' was horrific.

It had already been shown that the sirens, the mer-creatures, took whatever they wanted without care for human opinion.

He should have expected human faction to ally with them too, in love of blood, and of the sea, and entranced by the beauty of the creatures. He assumed there was more than one of them, at least.

These humans called themselves the Death Eaters, believing they escaped the kisses of the siren in their cult, and of its song in its deadly quality, by serving the creatures instead.

He should have expected that Green Lightning would be attacked too one day - not by sirens alone. He was becoming one of the most well known sailor's in Dumbledore's Army, fighting against the mer-creatures, taming the seas, alone because he could allow no one with him but those also immune.

They called his ship the 'siren ship' now, and he hated it.

The battle was bloody, and his only consolation as his ship was torn to pieces, everything flying, people throwing themselves into the dangerous waters to avoid the flames, was that at least he was causing due damage on The Dark Mark too.

There was chaos everywhere, shrieking, a vicious struggle to find wood and land and anything of substance as that song came, inevitably.

He managed to crawl onto driftwood with some other members of his dwindling crew, wishing he could block out the sounds of pleasure which turned to screams and blood in the water.

And then he was being hauled up out of the water, onboard, in a quick movement and dusted down, even as he thrashed and struggled instinctively.

If these were good guys, he didn't want them in danger - if they were bad, this couldn't mean anything good.

He was fighting, immediately, catching a glimpse of a female, the Captain evidently, with dark black curls and dark eyes, lips scarlet. He had a bad feeling at the resemblance to memories long ago, managed to fight free, killed one - couldn't believe he was actually leaping off the boat, and the next second everything went black.

* * *

Tom Riddle waited with a smug sense of satisfaction as his prize was brought to him; not that his petty little followers knew of the boy's truth.

If they knew they could use him so much more, he was sure they wouldn't have set him up as a mere offering.

This was how his lovely 'Death Eaters' worked, they targeted a naval ship, overtook it, and then set it on another under promise of death to the captured ship should it fail. Both ships went down, and his human pets picked up whatever loot they could, and whoever managed to survive the assault to bring them here, to the Siren port.

He stayed under the water, watching, head only surfacing in the shadows.

He'd been tracking this one for a long time now. He'd grown up well, and he knew he'd made a good investment, and had done so since he saw those pretty green eyes.

Of course, it was inconvenient when the boy continued to defeat and slaughter about a third of his kin under the delusion banner of the sea-dog, Dumbledore, but he did rather enjoy seeing the boy fight for his life.

It brought back such nice memories of their first meeting, of the boy's ruthless desire to cling to life.

He'd enjoy taming that spirit very much; after all, even with the whole ocean to rule after he killed Grindelwald, his creator, he needed something to do.

Harry's hands were bound, as were his ankle, and his beautiful Captain, Bellatrix, tugged the boy over the water. Harry's eyes had widened with the most delicious horror, as he realised his position.

"No! You can't do this," he thrashed. "Shoot me, hang me but don't put me in the water!"  
There was blood spilt, no doubt to draw him and his kin like bait, like an offering, and he smiled with some amusement, before emerging into view.

Harry went rigid at the sight of him, and it was almost a shame that he'd so put the boy off walking on beaches, like he'd often see him do as a child in that small village, and then he was struggling even harder.

"You'll continue to bless our ship and fortunes, my lord?" Bellatrix asked, breathlessly. She'd no doubt drown herself if he only asked her, and he gave her a smile in response.

"Of course, love," he purred. "Do we not have a deal?"  
She nodded, smirking back at him, and then, without any further warning, she shoved Harry forward so he crashed into the waters with a noise of absolute panic.

He couldn't swim, tied as he was, but he nonetheless struggled towards the surface, gasping for air.

Tom was on him in a second, diving, catching a foot and yanking him under, under and away, whilst the boy thrashed and tried to hold his breath and claw him.

It was amusing how those so strong on land could be so helpless like writhing fish when placed in water.

When the boy was about to expire, he let him bob up some distance away, coughing all over again as he broke the surface.

He was seriously tempted to spend the entire day drowning the boy, and saving him, in a vicious cycle. He'd always loved drowning, there was something about, the frantic desperation, the struggles that grew weaker with time, blue skin and lips.

"Hello Harry. I must say, you've grown up very well. I take it you remember me?"  
Even without him holding on, the boy kept going under, then breaking the surface again, restrained against swimming.

"You bastard, you can't do this-"

"Oh but we had a deal, and you've had three years extra already."

He grinned, tugging the boy out into even deeper waters, before untying him smoothly. Harry stared at him, wide-eyed, treading water, eyes moving frantically for any sign of land, and he smiled, back pleasantly. There was nowhere to go for miles around, he'd made sure of it.

"Take your time, Harry Potter. This part's always my favourite."

"Didn't anyone ever tell you it's rude to play with your food?" Harry spat in response, lunging for his throat. He dived, lazily, and the boy immediately let go. He caught hold of his foot again, amused, holding him just beneath the surface.

Bad manners, but ever so fun.  
It would be over by the time the sun went down.


	2. Chapter Two

Harry had been so close.

He was twenty one, it was his birthday tomorrow. If he could just survive the night...then even he died, he wouldn't become a siren. Tom wouldn't get the satisfaction of claiming him.

The creature circled him in the water, scarlet tail gleaming magnificent beyond measure in the late afternoon sunlight. Harry had remembered him being beautiful, his song lovely beyond all comprehension, and somehow reality managed to live up to the foggy memory of their first meeting.

But what did it matter if Tom was beautiful to more than a child's eyes? What did it matter that he hummed that seductive, wonderful, terrible song even now as he watched Harry tread water? Dunking him, holding him under, only to let him gasp for air again and looking at him like watching him nearly drown was the most exquisite thing he'd ever seen.

Harry didn't even have any of his weapons on him, to make it worse. The Death Eaters had stripped him of every last one, meticulously. So he struck out towards the shore, strokes strong and sure. It was a long swim, but he had to try, didn't he? He couldn't just tread water until his body failed him or Tom got bored and finished it.

"You know I will not allow you to reach land, don't you?" Tom smirked, flashing him those razor sharp teeth again. "You know you cannot possibly outswim someone like me in your current form. Though I do appreciate your efforts, your struggle to survive was one of the first qualities that drew me to you." The creature dove once more, and in a matter of moments his minutes of swimming had been dragged down to nothing. He was right back where he started, thrashing, as Tom released him to bob towards the surface.

This time, however, pale arms wrapped around him again.

Harry's jaw clenched as he seethed. He had three hours to kill the creature or he would become a siren too, and three hours where Tom would be most on guard to his attack.

But Tom didn't seem to be able to resist toying with him. Harry had found mer rarely could - the luring song was a game, but games didn't work with boys deaf to siren song, so they always got too close. Couldn't resist batting him around like a ball of yarn.

It had been the downfall of other mer, it would be the downfall of this one. He had to be clever about it though. Harry exhaled a breath to calm himself and twisted in the grip, settling his hand on the creature's shoulders.

"And how would you spend my last hours, then?" He studied Tom. "You've been waiting for thirteen years to make me yours, you've hunted me obsessively even when I cannot possibly be the only human you have marked. You must have made plans in that time."

"It's true, I have been rather busy since we last met," Tom said. "A mer does not become the ruler of the seven seas by chasing humans, however pretty the human." A sharp claw caressed his cheek.

Harry stilled. Ruler of the seven seas? But...no. "You said your name was Tom."

"It was, once upon a time. Nowadays I do tend to be known as Lord Voldemort, however."

Lord Voldemort. Harry sucked in a startled breath, fingers tightening on Tom's shoulders. It wasn't possible...was it? And was Tom boasting? He seemed like he was boasting, certainly looking for Harry to be impressed. He wasn't quite sure how he felt about that.

"I suppose I should be flattered that you came for me personally." Harry's mind raced through his options, heart pounding in his chest.

Tom flashed him another singularly lovely, singularly deadly, smile. "It is your birthday tomorrow, is it not, Harry?" the mer asked next, oh so slyly. "How could I not come for you personally on so a special an occasion? I think I like your timing, even if it was impudent of you to steal three years from me. There is a certain poetry to it."

"I wasn't aware your kind had much interest in poetry," Harry said.

"There is a lot you don't know about merfolk, Harry," Tom replied. "A lot your precious navy did not tell you. Let me give you a little birthday gift. Humans are fond of receiving presents, are they not?"

"Is this the bit where you say forcing me to become a siren is a gift?"

"I am not forcing you to do anything. We made a deal, one which must be honoured."  
Harry felt Tom's tail coil around him as the mer pulled back to examine him, seeming distinctly amused.

"I was eight!" Harry snapped before he could stop himself. He'd hardly been in a state to make lasting promises and conditions for the rest of his existence. Especially when it had been a take the deal or die sort of situation. "Under duress."

"Human notions," Tom dismissed. "You will come to lose those in time, and see the truth of what you are being given. You adore the ocean - even when most would flinch away, you would walk along the beach as a boy. I would see you doing it."

A shiver ran down Harry's spine.

"You currently live a half life at sea. You swim with your legs, you move on your ships always distanced from the waters you love. You have no community among men because you were never meant for them. No family, not even as a boy. They tossed you to me and yet you would call me the monster for taking you in?" Tom's head tilted. "Humanity have poisoned your mind and I am your cure, Harry Potter. When we first met you looked at me like I was the most amazing creature you'd ever seen. What precisely is your objection to becoming one of us?

"I have no interest in luring people and killing them," Harry spat. "Maybe that's my objection."

"All creatures kill and hunt to survive. Do you condemn the fishes too for their natural instincts, or does it only bother you when the hunter and the prey has a face like yours? I know you eat fish."

Harry's stomach churned as he searched frantically for a good response for that, but, as the seconds ticked by with just the crash and spray of the waves, a wicked smile broadened across Tom's lips again.

"Humanity would use you," Tom said. "Turn you against those who would embrace you most. I do not hold what you have done against you, I am a generous lord you need not fear. You were misled. Amends will be made."

Even if he died, a human, and never became a siren it wouldn't fix this, would it? There would be other eight year olds desperate to survive, other humans sang sweetly to their death, other sailors who died because their captain had been chosen by the sea.

Harry steeled himself. This wasn't just about saving himself, about killing one creature however important…

"How are you going to turn me?" he asked.

Something flickered in Tom's eyes - Harry struggled to place it, some mixture between suspicion and triumph - and the mer reeled him in closer.

"Flesh, blood and bone. I'll make a little cut right here severing your fragile human skin…" he traced a delicate, teasing line along Harry's neck, right where the creature's gills would be.

Harry's breath hitched.

"Feed you a little of my blood...break your human legs...drown you…" Tom whispered the last one like it was the most intimate act in the world, leaning in as Harry's heartbeat even faster."And wake you up again with a kiss." They were so close that some part of Harry itched to lunge, to claw Tom's silver tongue out with his bare hands if he had to.

"Sounds like fun." Harry wet his lips. "What are you waiting for?"

Tom could have done that already, it seemed a simple enough process. He wouldn't even have had to risk untying him.

The mer pulled back with a surprisingly serious expression on his face. "Changing you is worth nothing if you do not complete the ritual once the transformation is complete. Your co-operation is helpful, as much as I am more than capable of ensuring you complete the ritual myself."

Harry swallowed, fingers flexing. "And what does completing the ritual involve?" He had a strange feeling that he wasn't going to like it.

"As you might imagine...flesh, blood and bone. Specifically, you luring and devouring your first human."

He was right. He didn't like it - at all. Could he really do what was necessary to take down the sirens completely? He'd always counted on the possibility of simply eating fish, instead of humans. Now...now he wasn't sure that was an option. To survive and not kill.

He supposed it explained why his mother had wasted away, instead of trying the same.

"Of course, there is also the fact that the ocean is a dangerous place," Tom said. "There's nowhere to hide, particularly, and the competition is more ferocious than anything you will see on land. Miles upon miles of open water...there is no room for civil war among my kind. There is little point in changing you if you are simply going to make my life needlessly difficult, I have a kingdom to rule and no intention of losing the throne.

Did Tom...know his plans? Certainly, he seemed to at least anticipate the possibility of a coup. Harry dared not look away as those pitiless eyes examined him. He raised a brow instead.

"So you were waiting for me to give my...consent?" It seemed a strange notion, from creatures whose mere voice obliterated willpower and ensnared humans entirely. It threw him off guard and Tom looked like he knew it, just like he knew Harry didn't expect sirens to have much appreciation for poetry.

"Do you?"

"What happens if I say no?"

"I'll drown you," Tom said. "Life or death, you agreed to be mine. As I said, deals must be honoured."

Harry considered his options, though it seemed pretty bloody obvious. Change. And then rebel later, civil war regardless.

It seemed simple enough, in theory. Except that still didn't account for the fact he had no desire to lure people and put them under his spell just by speaking. Not to mention the process sounded generally awful, and the thought of drinking siren blood made his stomach turn.

But what other choice was there? Die, and let some other eight year take the fall, let the system continue because he was too stubborn to do what was necessary?

No.

"Yes," Harry said, mouth abruptly dry. He never imagined he'd be saying that three hours ago.

Tom smiled at him and it wasn't remotely reassuring. Perhaps because for all the unholy glee on the creature's face, there still seemed something cold and ferocious to him. The something that made him fine with tricking terrified eight year olds into ancient contracts.

The water around them seemed to pick up, the faster churn of a storm that hadn't been brewing or anticipated a few seconds before.

"Relax then," Tom crooned again, trailing a claw up to guide his head back, exposing Harry's throat. "I'll look after you. Are you always so tense?"

"Only when I feel like I'm signing my soul away to morally dubious sea creatures," Harry said.

Tom laughed then, eyes gleaming. "The sea is a cruel mistress, Harry. It does not believe in human ideals of morality and fairness, how can you expect her children to be any different?"

"Just get it over with." Harry peered up at the sky, jaw clenched, the burnt orange of the setting sun dipping into glorious reds and bruised-purples on the horizon. The water lapped at him, as if eager to consume him too.

Tom's claw sliced in a heartbeat. Harry felt the emotion, but it took a second for the pain to hit. Then he gasped and choked, jerking in the water. His hand rose instinctively to clutch his throat and put pressure on the wound. Tom grabbed his hand, tail grip tightening on him in an instant holding him still and pliant as he shuddered. The mer's dark eyes seemed large and bright and hungry.

Maybe he'd made a horrible mistake. It was too late to go back, wasn't it?

The water around them tinged pink.

"Hush," Tom breathed against his ear, clutching him even closer against his chest. "Be still. I've always had you, hadn't I? I delivered you to salvation before."

A cool tongue dragged along the bloody cut on his neck, and Harry struggled to flinch away because he was pretty sure Tom hadn't mentioned anything about that! The mer hummed, an utterly pleased, self-satiated and seductive sort of sound in his ear. He had no idea if Tom was aware of it or not.

"You taste delectable," Tom said. "I think I would have chased you even if you weren't destined to be one of us. It's a pity really, that our kind always have the best flavour, though it makes you easy to find. Your first siren call."

Harry wanted to talk, but with a slit throat it was rather difficult. He settled for glaring as Tom met his eyes again, lips stained with Harry's life. This time, the smile he flashed was utterly predatory - no pretense at charm, just sharp teeth. His whole body felt as cold as if he'd been left in arctic waters.

Then Tom bit down on his wrist before shoved the offending appendage against Harry's mouth.

For a second, the wild urge not to drink bucked in Harry's chest again. A frantic sound escaped him. The second after that, the blood trickled down his throat. A small thread of warmth, a hook, the best ambrosia Harry had ever tasted in his life...and before he'd even thought about he suckled greedily. Eyes fluttering closed.

The world seemed distant, far-away, the Death Eaters and the events that led him there a dream.

It was over quickly, Tom tugging his hand free. "For someone objecting to murder," he teased. "You have quite the siren's appetite, Harry." The broken legs came without warning, before Harry had even finished blinking dazed and disorientated.

Tom's tail twisted.

The cry wrenched out of Harry's bloodied lips.

Tom dragged him beneath the waves, studying him intently as all surface sound faded away. Instead, Harry could hear the song louder now, that beautiful eerie song that had been haunting him since he was eight years old. It roared in his head, overwhelmed him as bubbles issued from his mouth.

He strained instinctively for the receding surface light, for air, as Tom dragged him down steadily into the darker depths of the ocean. His vision blurred. Black spots sparked in his vision. Everything hurt except for the small throbbing ball of heat inside him.

The blood spiralled and coiled upwards in the water from his neck - a scarlet hangman's noose.

Tom stayed close as Harry's life slipped away with each second that passed.

Hadn't he said something about a kiss? Tom was breathing. Tom had oxygen, of a sort, however stale and strange. Harry needed it.

He lunged forwards, only for Tom's fingers to curl in his hair.

 _Not yet._

Tom couldn't possibly have spoken aloud, but Harry heard it as clearly as if he had.

He could hold his breath no longer. The water flooded his mouth, sharp and cold in comparison to the heat of mer blood. His body spasmed again, jerked, only inhaling more dizzying water as Tom watched him eagerly.

His chest burned.

Tom trailed soothing fingers along his cheek and kept singing.

Harry's struggles began to lessen, body exhausted and bled out. His mind surrendered, settled calm. His eyes fluttered closed.

Lips ghosted against his own, before closing. Drawing him in impossibly closer, until Harry felt like he was in the coils of some monstrous sea serpent, until he felt they were fused.

The heat burst inside of him. The tingling sensation pulsed through him as their lips stayed pressed together. He moaned into Tom's mouth, tasting salt and copper. The spray of a wave, and Harry was falling, falling, falling into it…

It no longer hurt. If this was drowning, Harry could spend the rest of his life drowning in Tom's arms.

This time, Tom didn't stop him from reaching up a sluggish hand to his neck and the gills forming. Sharp claws shredded his clothes away - but Harry had no room for self-consciousness or embarrassment. Hands claimed every inch of him, the hungry mouth kissed him like a feast long denied.

He wasn't entirely aware of when Tom stopped kissing him, but suddenly there were teeth and lips at his shoulder, nipping and worrying at soft skin until it wasn't soft anymore.

Harry felt strong.

Fingers smoothed over his hips as skin turned to scale...gleaming, emerald scales and forest green scales and seaweed coloured scales.

The next thing Harry was conscious of was hunger. Ravenous, cavernous hunger as if nothing in the whole world could ever fully fill him up or satisfy. Hunger like fish hooks lodged into his chest, tugging him to hunt, to sing, to lure. Hunger like hunger was all that was left in him.

He scanned the ocean with clear eyes, tail twisting this way and that.

His gaze landed on Tom.

 _Go on, Harry._ The siren' voice felt like a song in his head, impossibly richer and more nuanced than anything he could ever have comprehended as a human. _Impress me._

Harry was off in a flash the song erupting out of him like vengeance.

* * *

When the fog in his head cleared Harry stared in horror at what he'd done. The shipwreck - the Dark Mark - lay in tatters around them. Bones picked clean and drifting towards the ocean floor, other creatures taking advantage of the carnage too great even for Harry's appetite.

The sea washed away the blood at his mouth, the murder on his hands.

Dozens of lives, and all because of his song, of his body a blur in the water that wreaked devastation.

 _Perfect._ Tom again, a song of satisfaction and delight and wonder. _I knew you would be, it's why I picked you. All that power. You are beautiful._

Harry shuddered, twisting his head this way and that as if he could shake the words and the voice right out of his ears. "I wasn't myself! I don't know what came over me - I couldn't think -"

It didn't come out as words, just bubbles beneath the water. He clutched at his mouth, his throat.

 _It's alright, you'll learn. The song isn't in your mouth it's in your soul. You will adapt quickly, I know it's overwhelming at first. I'll teach you everything you need to know._

"Where are you?" more bubbles. Harry couldn't see through the wreck, the husk of his enemies. At least it was Death Eaters and not a naval ship. Was that because they were closest or because some part of him had considered?

Harry wasn't sure he knew which was worse. Everything was the song - calling, calling, calling at him. A war drum in his head and he'd never expected that.

Tom appeared at his side, the only familiar thing and Harry thought he knew the ocean like home. The mer caught his hand, guiding him along until they were in clear water as well. He could see other sirens at the shipwreck now, feeding, harvesting, he had no idea.

 _I killed them. Did - was that all me?_

He couldn't let this happen again. Screw his plans, screw taking sirens down from the inside, he'd beach himself. Surrender himself to the navy. Sing sailors to safety instead of doom, like his mother. How could he have done this?

 _It was your song._

Wasn't that the same thing? Tom said it like the song was something separate, beyond his control. Nobody had ever mentioned anything like that, ever. He stared at Tom, wide-eyed and shaken.

 _Come._ Tom released his hand, grace embodied in the water as he spun and dove. _I'll introduce you to your family._

Harry didn't know what else to do, so he followed.

* * *

 **A/N: So this is half repost of an old story I took off FFN, and half a new chapter. The reason for the repost is the new chapter seeing as this isn't just a random floating oneshot anymore, I hope you enjoy it and as always I'd love to get your feedback. The next chapter will be the last.**


	3. Chapter Three

The last few weeks had been a whirlwind of new information and new faces.

Mer had entire cities beneath the waves that Harry had never known about or even suspected, infrastructure beyond what humans had ever believed possible.

 _Magic._ There was no other way to describe it.

It was, admittedly, one of the most brilliant things he'd ever seen.

And everywhere, everyday, there were songs.  
He'd always thought the siren song was intended solely to hunt humans, to lure prey, but the mer had songs for everything.

Songs for pleasure, songs for delight, songs for communicating victory.

Songs of sorrow, of pain that made his whole body clench with the shared grief of one of their number being killed or captured by human fisherman or naval officers.

Songs for healing, songs for building, songs for reassurance and friendship. Songs for everything public, if thoughts were private and personal.

Beautiful, eerie, exultant song that filled Harry up inside like the only familiar sound in the world. It was impossible not to be affected by it.

/It's overwhelming, isn't it?/ A familiar voice drifted into his head.

Harry turned a fraction, not expecting anyone to find him. Most the mer, when not out hunting, tended to stay within the protected limits of their communities. Most the mer loathed him, they knew too well how many sirens he'd taken down while he was still a human. Tom didn't loathe him - Tom thought he was beautiful.

Apparently even by Siren standards, he was dangerous.  
He wasn't quite sure how he felt about that.

Either way, it was good to get away from the stares when Tom wasn't there to distract him, as he was prone to do, and Harry enjoyed the ocean stretching far as the eye could seen on every side. Relished in the feeling of the water on his skin and the peacefulness of it all. He enjoyed heading towards the glittering kaleidoscope of light at the surface too, to burst through it and see the shore and watch people, even if it was risky. To guide ships in the right direction, when he could.

He liked going down too, scooping up handfuls of undisturbed soft sand and letting it trickle away again.

He loved the ocean more than ever before with every second he spent between the waves.

The mer beside him _looked_ familiar too, with ginger hair streaming behind her and a tail like a sunset. It took Harry a moment to place her, before his eyes widened.

/Ginny/.

Ginny Weasley had gone missing during Harry's second year as the captain of Green Lightning. He'd never met anyone as talented with a ship as her. They'd met at port - she'd been investigating siren song. Rough calloused hands and soft lips and laughter. The absolute antithesis to the song, to Tom, ensnaring and seductive and complicated.

He never even knew she'd been marked too.

/Hello Harry/.

Questions raced through his mind - the how's, the why's, the what's, the who's. A small sharp toothed smile crossed her face and he thought his confusion must have been obvious.

/Tom turned me two years ago. I wanted to learn more about the song, there is no better way to do that than to live it personally. I think he wanted to learn more too, he's fascinated by it./

/Is it always so overwhelming?/ Harry asked.

He'd managed to not wreck anymore ships despite Tom's best efforts and encouragements that he should embrace his power, but that particular song tugged right at his very blood. Constant, inescapable. To hunt, to lure, to feed.

Sometimes, he could barely think through it and it was all he could do to resist the call and not let the song burst out of him. It made it hard to focus on his plan of siren civil war and downfall. Sometimes, as he got to know the sirens - to watch them interact with each other with the same warmth and complexity as humans did - he didn't even want to.

/Yes, though I believe yours is particularly powerful as you're no doubt aware of by now. It's probably why he picked you./ Ginny hesitated. /You might have gathered by now that the song is yours, but also not yours./

Harry remembered it all too viscerally.  
Tom sang to him, and he'd lost all control.

Ginny looked around, even if there was nowhere to hide and no one in sight, before leaning in a little closer all the same. It was a strangely human tic that ached in Harry's chest, compared to the graceful perfection and utter functionality of all siren movements - they never made a movement they didn't consider utterly necessary. It made sense for the ocean. Humans were wasteful by comparison, gluttonous.

/Siren song is quite communal, you might have noticed, even if we all have our own personal and private songs too. Just like oceans are all made of water, but the individual sea may be different and have a different temperament. Communities have leaders, and their song and vision shapes all of us./

Tom's song. Lord Voldemort's song.

/Normally the leader of the sirens does not turn anyone personally for that reason. There is a connection between sire and the siren he created, a bond so to speak. He turned me before he became Lord Voldemort, but you.../ Ginny stared at him.

Harry's stomach lurched. /Why did he turn me, if that's not normally done?/

Ginny's tail twitched in a way that Harry had come to understand as 'no idea'.  
Either way, it wasn't particularly reassuring.

/Why are you telling me this?/ he asked instead.  
Ginny's caution certainly suggested that perhaps she wasn't supposed to be sharing the information with him, and anyone else he'd asked about the song had always dodged his questions or started talking about his amazing feat with the ship.

/Not all oceans are dark and fierce and bloodthirsty. Some are gentle sea foam and soft sand and turquoise waters so clear you can see the coral at the bottom./ Ginny's head tilted. /Maybe not all siren songs have to be dark and fierce and bloodthirsty either. You know they aren't, you've heard songs of peace and happiness as well as war and rage. Sirens do not have to eat humans. It's because of his song that they feel compelled to./

/So if someone else's song shaped the siren community.../

/Then maybe my brother and hundreds like him wouldn't be dead./

Harry wondered, for the first time, how many people had turned for the exact same reason as he had, only to buckle beneath the force of the siren song they were no longer deaf to. Turning left those immune even more exposed than any human ever was.

He wondered if Tom had planned it that way.

* * *

Tom under the ocean was a wonder to watch.

Where Harry assumed the novelty and the beauty of him would finally fade when he too was a siren, it simply wasn't true. Even by the standards of mer Tom seemed to be something else.

He didn't know if it was because Tom was Lord Voldemort, ruler of the sirens. Or if it was something uniquely Tom, with nothing to do with his position. Being a siren didn't change a person's actual face or brain after all and Tom had particularly handsome features.

At least it wasn't just Harry who thought so.  
The memory of their kiss drifted through his mind too often.

/I hear you have been asking questions about the song and my rise to power./ Tom's voice sounded as rich and intoxicating as it always was.

The other mer around them scattered under Tom's glance, leaving the immediate ocean around them empty as they moved to different parts of the city. Tom came to a stop next to him, body half curled around his in the water.

Harry stilled, claws flexing. Uneasy with the way Tom was looking at him.

/I was curious,/ he said.

/Naturally/. Tom flashed him that charming smile again, even as his eyes remained calculating. /You always are./

Harry flashed him as oblivious and charmed a smile back as he possibly could. He shifted to put some distance between them, but stayed calm. Maybe as a human he'd been lost in the water, but they were on the same damn level now. Equal.

Tom didn't look like he bought it for a second, shifting even closer. His tail curled lazily in the water around them, like a coiled serpent. /What precisely were you curious about?/

/Scared I'll try and take your job?/

/As if you could/. This time, Tom's voice came like the crash of a wave in his head, and Harry nearly flinched at the force of it. It softened a moment later. /You are powerful, Harry. I am not denying that, I never have. But the sea has no space for your human moralities and I would not force you to change. You are perfect the way you are./

Harry had been about to say something that was no doubt unwise, about how funny and convenient it was that Tom got to decide what there was space for in the ocean, before the last comment brought him up short. If he had breath underwater, it would have hitched.

/That's not the first time you've called me perfect./

Tom's smile seemed less falsely charming this time, and somehow sharper. /No, but you always find new ways to remind me./

/I killed dozens of mer, your people hate me./ Harry said it like a challenge, his head spinning. He'd expected a fight when Tom approached him, a struggle for dominance and Tom threatening him, but there didn't seem to be any of that and he didn't quite know what to make of it. He'd geared up for a fight. Maybe when he was destroying human ships he could understand why Tom would think he was perfect, but now? /Why did you turn me?/

Tom's head tilted at the question, an eerily reptilian gesture. /We had a deal, a deal must be honoured./ he said.

/I heard the ruler of sirens didn't turn people./

/And who told you that, Harry?/ Tom's smile was the sweetest he'd ever seen, and Harry's eyes narrowed. /I admire a healthy curiosity./ Tom's voice, too, was an almost purr in his head, more silken and seductive than ever before.

/You admire a healthy curiosity...but you won't answer any of my questions, and funnily enough no one else will either./

/Someone must have done./

/No one of importance./ Harry shifted, as Tom circled him in the water. /If you admire curiosity so much, fill in the gaps./

/How can I do that when you won't fill me in on what you know already?/ Tom returned. /Besides, nothing is free in this world. We wouldn't get very far if it was. How about an answer for an answer?/

Harry's jaw clenched, mind racing through his options. He was certain that deal tilted in Tom's favour. Tom knew more, he had more to trade with.

But maybe, just maybe, if he guarded his secrets so fiercely he had more to lose too. The worst Tom could do to him was kill him, and that had been a possibility when he considered drowning rather than transforming in the first place.

But Ginny could get hurt.

Dozens of humans got hurt every day under the siren song.

He might only get one question, he'd have to make it count. But what question?

Harry jutted his chin up. /Deal. An answer for an answer. What was the real reason you turned me? You could have sent any of the others to do it if it was solely about the deal. You didn't have to do it personally. There's a bond, between sire and siren, you never mentioned that before./

Tom stayed silent for a moment, seeming surprised that Harry asked that question out of all potential questions.

/Yes. There is a bond, one largely unexplored by someone in my position as your informant told you. Swim with me…/ Tom began to move, leaving Harry to keep up as they left the siren city behind. Instead, they swam into deeper, darker, colder waters which cloaked them like shadows.

It wasn't particularly comforting - it felt more like the ocean equivalent of being lead down a suspicious alley in order to be quietly disposed of.

/I knew you would be powerful,/ Tom said softly. /It was obvious from how strongly your blood called out when we first met./

/My first siren call, you said./

/Yes./ Tom glanced at him, even and considering. /Land and sea are at war, humans and sirens are at war. You know this. It is the reason you consented to the change, hoping to fix that problem, yes? No matter what it took to do so? I'm not stupid, Harry. I know you have been plotting ways to overthrow me ever since I turned you. You have your informants and I have mine./

Harry's stomach twisted but he kept his expression as blank and unreadable as he could. Tom didn't seem to be expecting an answer, though he watched Harry closely.

/Sirens rely on humans to survive./ Tom continued. /Maybe one in a hundred humans are born with the capacity to change, and we are fortunate that so many are born on the coastline, but not all of them. We are still trying to evaluate what precisely causes some to be born with the song, and others not to be. Meanwhile, our forces dwindle year by year. You know this too, you have killed hundreds of sirens during your career as a naval officer. So you can imagine that the continuation of our species is quite the problem./

/And where do I come into this?/ The long-winded response wasn't the simple and evasive answer Harry had anticipated.

/Your mother was a siren,/ Tom said. /She was pregnant with you when she transformed. I believe you may hold the key to a new way of creating sirens./

After all the dodging, all the refusals to answer his questions, the bluntness of the response took Harry by surprise. His mouth went dry and he froze, tail curling in the darkness. His heart hammered in his chest.

/Meaning?/

/Ah ah, it's my turn to ask a question, I believe./ Tom flashed him another smile. /Who was your informant?/

/Are you going to hurt them?/ Harry demanded.

/So many questions./ Tom practically crooned now, eyes gleaming in the darkness. They weren't the eyes Harry recognized, they burned like hellfire. /I want my answer, Harry. You owe me an answer, that's how this works./

Harry stayed silent, before answering reluctantly.

/Ginny Weasley./

/Thank you./

Harry darted forwards as Tom turned, seizing hold of a pale wrist. /Don't hurt her./ It wasn't a plea, he didn't mean it like that. He meant it like I'll rip your lungs out with my bare hands if you touch her. A song of command and warning and fury that saturated the water between them. /You admire a healthy curiosity, don't you?/

Tom's pupils dilated, dark and alien.  
/You knew her, as a human. She talked about you a lot. Is that why you are so protective of her?/

/I'm protective of her because it's the right thing to do./ Harry paused, considering Tom's answer still. /Is that why you changed her personally?/ he ventured. /Because I knew her?/ It sounded arrogant and self-absorbed to even suggest it, and yet…

It was impossible for the sea to crackle, to taste a storm in the water, but the hair on the back of his neck stood on end as their gazes locked.

/It was one of many reasons,/ Tom said, softly, like he was confessing something intimate.

Harry wet his lips, and the song swelled in his head, itched in his bones, and - and - the moment broke as Tom looked away. His gaze slid down to Harry's grip on his wrist.

Harry let go somewhat automatically, like he'd been scalded.

Tom turned away once more.

/You're a bit obsessed with me, aren't you./ It slipped out before Harry could stop it but it did get the Tom to stop once more. /Because I can somehow help you create new sirens? How am I supposed to do that when I don't know your plan?/ Harry pressed. He wasn't, frankly, sure if he wanted more sirens in the world if they would be such dark, bloody creatures under Voldemort's siren song.

Somehow, impossibly, Harry only had more questions now than he'd started out with.

/Would you like to make another deal?/ Tom asked. And this time, when he looked back, Harry knew he hadn't imagined the scarlet in the siren's eyes. /Let me worry about everything, and Miss Weasley will be perfectly safe. Turn this into a war, and I'll give you casualities starting with her tongue in your sleeping pod. You want to keep everyone safe, don't you?/

Harry's insides chilled.

That time, he didn't stop Tom from swimming away.

* * *

Carnage stained Harry's hands.

The ship sunk towards the bottom of the ocean, the bodies floated in the water with the flesh stripped right to the bone.

Harry could feel the song differently now; feel it humming satiated and delighted in his blood and in the back of his head and in every inch of him like he could drift spent and high.

His stomach revolted, his mind flinched, his heart sank like a stone.

This wasn't supposed to happen again.  
Yet every day, the song - the bond between him and Tom - seemed to only grow stronger. He didn't know what Tom was doing.

He hadn't even talked to the Siren Lord in months, hadn't talked much to any of the other mer. So much for his brand new family under the sea.

Of course Tom found him now, as the city swarmed on the spoils of his hunting.

/How does one become the leader of the sirens?/ Harry asked, before Tom could say anything. He wasn't sure he could deal with the other's praise right then.

/Still curious?/

/Did you expect me not to be? I've behaved, haven't I?/ Harry spat.

Tom hummed, a crooning soothing sound.  
/Curiosity is admirable, ignorance is bliss. If I told you, you would only feel compelled to sacrifice everything for a humanity that no longer wants you, that never wanted you, out of some remnant loyalty to what you used to be. You would not be able to help yourself from playing the hero, even if you would not enjoy being me, Harry./

/I wouldn't be you./

/You imagine you would be soft sea foam and gentle waters if you took my job?/ Now Tom sounded mocking, a smirk on his lips that left Harry frozen. /You know as little about peace as I do, Harry. Look at what you just did./

/Because of your bloody song!/

/You slaughtered hundreds long before I ever turned you./

Harry opened his mouth to protest that - but it had been his reaction to finding out his future hadn't it? He'd hunted sirens. /I was protecting people,/ he managed. /Humans./

/And now you're a siren, yet you condemn yourself and me for feeding and protecting your own kind?/

/Sirens don't have to feed on humans./

/No, they do not./ Tom agreed with an ease that gave Harry pause. /Just like humans do not have to slaughter sirens, pour oil in the ocean, and fish to the point of causing irreparable damage./

/So it's revenge?/ Harry bit out. /Who does that help?/

/It's pest control/ Tom replied. /If they truly wanted peace, all they would need to do is move away from the coasts, so they cannot hear the song./

Harry stilled at that. They stared each other down, equally unyielding.  
/They have just as much right to be there, it's land./

/They can have the coast if they stay on land, as you are intimately aware - they do not./

Harry narrowed his eyes, but couldn't actually think of a good response to that.  
/Our bond has been getting stronger. Why? Where do I fit into any of this?/

/You are a prototype./

/To create more sirens./

/Ten years is too long a time to wait for the deal, it allows sirens to grow too used to the facade of humanity. It is allows them to convince themselves that they are humans changed into sirens, not simply sirens taking their true form./

Which was, to Tom's mind, Harry's problem. Harry who had been born of a human father and a siren mother. /And that involves me slaughtering ships...why?/

/All of the ships you have slaughtered have had potential sirens on,/ Tom said. /Sirens you have since bitten./

/Sirens who are dead and drowned./

/No,/ Tom sang out, delighting in Harry's surprise. /You have never actually looked at the carnage you create, have you? You are always too busy feeling guilty about it and trying to get as far away as you possibly can from the scene of your crime./

/Flesh, blood and bone./

/Your bite is a rather potent and interesting alternative,/ Tom said. /Considering what you are. Considering you are connected directly to me, too, thus furthering my blood line too./

/And the connection between us getting stronger?/ Harry felt lightheaded.

/Of course, the process still needs tweaking and I don't think you're quite safe to set upon the coasts yet,/ Tom said. /So far the only ships you have deigned to go for have been pirate ones./

Harry's stomach dropped. The plan became clear, and if Harry had anything in his stomach to throw up, he would have done.

/And not the little eight year olds that you want to turn and raise as your own. Which is why you wanted - needed - the sire bond to try and influence me. Whether I like it or not./

/You are the most exquisite weapon I have ever seen,/ Tom murmured. /With me to wield you, you and I are going to change the world. Being a siren in your blood, Harry. In your bones and your flesh and your soul. I did promise you a brand new family under the sea, did I not?/

As the rage coalesced in Harry's song, so did the song and Tom smirked rather smugly.

/Deals go both ways,/ Harry warned.

* * *

/They're not very bloodthirsty. What did you do? _What did you do?_ /

/They're not just yours,/ Harry replied. He met Tom's gaze with blazing eyes. /Guess I'm not as good a _weapon_ as you thought. Weapons don't fight for peace, do they? You were wrong./

Tom spent a long time watching him after that.

* * *

Ten years passed.

Ten years of battle and negotiation and slaughter and rebirth. He grew to know Tom rather well in the ten years of them working together.

The siren communities thrived, over-spilling with new life and young blood and a new brand of sirens that thought little of humanity.

Views about children deaf to siren song changed too. The Ministries had passed their solutions - offering up siren children to avoid having them hunted by force.

Between him and Tom they'd managed a strange sort of peace, or maybe a stalemate. Either way, the attacks on the coasts had stopped. It was Harry's demand for going along with Tom's plans, in the end.

They rebuilt. Cities spread under the ocean. He and Tom found something of their own, strange sort of peace between them. It was impossible not to, with how closely obsession and song kept them entwined.

Now, Harry had finally found out the secret of becoming the ruler of the seven seas after all that time. Tom Riddle became Lord Voldemort, and sold his soul to the ocean in return for its power. As ensnared by the song as any of them, or maybe so.

But Harry had always been born of the sea, so maybe Tom Riddle sold his soul a little to Harry too.

It wasn't quite sea-foam and turquoise waters, but sometimes it was.  
The sea had never been quite one thing or the other, had it? And maybe neither had siren songs.

* * *

 _A/N: So this chapter was a bit of a nightmare to write, mostly because of the sheer amount of ground to cover without completely tipping the structural balance of the story. I was aiming for something a bit more like the first chapter, but I don't know if I managed the same feeling or not. Either way, I hope you enjoyed the story!_


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